NEW: Nominations are now open for the 2019 Swift Community Awards! >>

How to add a custom initializer to a struct without losing its memberwise initializer

Swift version: 5.1

Paul Hudson    @twostraws   

All structs in Swift come with a default memberwise initializer, which is an initializer that accepts values for all the properties in the struct. However, as soon as you add your own initializer to the struct that memberwise initializer goes away, because it’s possible you’re doing special work that the default initializer isn’t aware of.

If you want to keep both the default initializer and your own custom ones, there’s a simple trick: create your initializers inside an extension rather than as part of the main struct definition.

For example:

struct Person {
    var firstName: String
    var lastName: String
}

extension Person {
    init(name: String) {
        let split = name.components(separatedBy: " ")
        firstName = split.first ?? ""
        lastName = split.last ?? ""
    }
}

Because my custom initializer is inside an extension, you can create instances of Person in two ways:

let taylor1 = Person(firstName: "Taylor", lastName: "Swift")
let taylor2 = Person(name: "Taylor Swift")

SAVE 20% ON iOS CONF SG The largest iOS conference in Southeast Asia is back in Singapore for the 5th time in January 2020, now with two days of workshops plus two days of talks on SwiftUI, Combine, GraphQL, and more! Save a massive 20% on your tickets by clicking on this link.

Available from iOS 8.0 – learn more in my book Swift Design Patterns

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.8/5